I have a 2000 S40 and noticed that there is what sounds like a whirring sound coming from the front of the car (or maybe the dash or center console) after startup and sometimes when reversing. It lasts for about one second and occurs several times. It sounds like an electric motor. Could it be the auto climate control opening or closing a valve? I'm wondering about that because the air recirculation is stuck in the open position.

I've had this car for only a few months so I don't know how long this has been going on. And it's my first S40...quite a change from the 1984 240 I've been driving for 26 years!

I can't think of anything that going into reverse would have to do with a whirring sound - perhaps its just the timing of you shifting gears or going into gear is dropping the system vacuum and the aux vacuum pump is kicking on. On my 2000 S40, The vacuum pump kicks on and off a few times after a cold start to build up brake booster pressure. Its possible you could have a blend door motor trying to sync itself. Rather than a stuck door, I'd suspect the actuator arm from the motor to the door may have unhooked itself.